Federal investigators are probing allegations that Carrier IQ software found on about 150 million cellphones tracked user activity and sent the information to cellphone companies without informing consumers, according to government officials.

The controversy over the software company, based in Silicon Valley, erupted a few weeks ago when security researcher Trevor Eckhart discovered evidence that a piece of software developed by the company and found on smartphones captured every keystroke and text message written by users and sent the information on the handsets to carriers.

The FTC inquiry was confirmed by officials who spoke on condition of anonymity because it is private. An FTC spokeswoman said she could not confirm or deny whether the agency was investigating Carrier IQ. But a spokesman for Carrier IQ said company executives were cooperating with federal agencies.

“This week Carrier IQ sought meetings with the FTC and FCC to educate the two agencies . . . and answer any and all questions,” said Andrew Coward, the senior vice president for marketing, adding that he was “not aware of an official investigation.”

Earlier, Mira Woods, a public-relations contractor for Carrier IQ, wrote in an e-mail: “We are complying with all investigations at this time as we have nothing to hide. . . . We have been completely transparent through this process.” In a follow-up e-mail and conversation, she asked The Washington Post to change the word “investigations” to “inquiries.”

Carrier IQ has said that its software is not designed to capture keystrokes or the content of messages but that in some cases that might have happened by accident. The data are intended to help improve the user experience with smartphones, the company said.

Three of the four major cellular providers — AT&T, T-Mobile and Sprint — have said they use the company’s software in line with their own privacy policies. A Verizon spokesman said the program is not on any of the company’s mobile devices. Apple has said it would remove Carrier IQ from i­Phones in a future software update.

Rep. Edward J. Markey (D-Mass.) asked the FTC on Dec. 2 to investigate the practices of Carrier IQ as possibly unfair or deceptive. “I have serious concerns about the Carrier IQ software and whether it is secretly collecting users’ personal information, such as the content of text messages,” said Markey, co-chairman of the Bi-Partisan Congressional Privacy Caucus. “Consumers and families need to understand who is siphoning off and storing their personal information every time they use their smartphone.”

Markey, in a letter to FTC Chairman Jon Leibowitz, said the Carrier IQ software raises a number of privacy concerns for smartphone users. Leibowitz could not be reached for comment.

While Carrier IQ executives were meeting with federal regulators, another controversy about the company erupted in the blogosphere. A response by the FBI to a reporter sparked rumors that the bureau was using the software for domestic surveillance.

The FBI denied a request for information regarding Carrier IQ filed by a reporter for MuckRock News under the Freedom of Information Act. The reporter had asked for “manuals, documents or other written guidance used to access or analyze data” gathered by any Carrier IQ program. In denying the request, the FBI said it had information but could not disclose it, because it was considered “law enforcement records.”

“The information you requested is located in an investigative file which is exempt from disclosure,” the FBI wrote to reporter Michael Morisy. FBI spokesman Paul Bresson declined to comment on whether the FBI was investigating Carrier IQ or using the software for surveillance purposes.

Carrier IQ released a report that shows the company collects information about carrier networks, data transmission speeds, phone numbers called, Web sites visited and battery life. The company also released a statement about Carrier IQ and the FBI, saying that the data are “not designed for law enforcement agencies and to our knowledge [have] never been used by law enforcement agencies.”

“Carrier IQ [has] no rights to the data gathered and [has] not passed data to third parties,” the statement said. “Should a law enforcement agency request data from us, we would refer them to the network operators. To date and to our knowledge we have received no such requests.”

Carrier IQ first came under scrutiny on Nov. 28 when Eckhart posted a YouTube video, explaining his discovery that Carrier IQ records information about app activity and battery life and appeared to take note when users press any key on the phone or when they compose text messages.

The backlash following Eckhart’s research has prompted several lawsuits against the company, mobile carriers and handset makers, including two class action lawsuits in Illinois.

A class-action lawsuit has also been filed against AT&T, Sprint Nextel, Apple, T-Mobile USA, HTC, Samsung, Motorola and Carrier IQ by mobile phone customers in Delaware.